In the fabrication of dental prosthetics, such as false teeth or caps, a negative impression is made of the teeth of a dental patient using a thermoplastic material. The negative impression is then filled with a hardenable material to form a die. The die is affixed to a base formed of similar hardenable material to form a dental model. A dental model articulator is used to correlate upper and lower dental models in the forming and adjustment of the dental prosthesis.
The appeal of using a one-use or dispensable articulator is one primarily of time. A reusable articulator needs to be mounted to the models of the teeth with dental plaster, which requires considerable time in the processes of mixing, placing, curing, clean-up and then the subsequent removal of the hardened plaster from the models and articulator after completion of the prosthesis so as to allow re-use of the articulator. Dispensable articulators can save the time involved with these steps and have the added advantages of allowing the completed work to be returned to the dentist still articulated to allow verification of the mounting and to increase the presentation value of the case. Typically, a one-use articulator is secured to the dental models using an adhesive, thereby eliminating the use of plaster. To allow this, the articulator must provide a mechanism to adapt glueable members to angular differences of surfaces on the models. Such a mechanism is not needed as part of a reusable articulator because its members are allowed a large range of angular and positional differences within the masses of plaster that are used to affix the articulator to the models.
Multiaxial adaptation is a primary consideration in designing a successful one-use articulator. One approach is to use an adaptive pivot mechanism that allows multiaxial adjustment between a hinge and one or both models. U.S. Pat. Nos. 4,382,787, 4,865,544 and 5,425,636 disclose articulator designs that adapt to the models using ball and socket joints which are then immobilized with adhesive or friction. This approach forces a tradeoff, in that the joints must be kept small in order to provide the required amount of angular adjustment which in turn reduces the surface area of the joints, thereby limiting reliable immobilization.
Another approach of adaptation is to use an extensible member or members and allow adjustment of these in conjunction with a hinge joint axis to provide accommodation of these glueable surfaces to the differences of the orthogonal axes that share each of the top and bottom surfaces of the models. Accommodation of the remaining axes of difference orthogonal to these surfaces is accommodated simply by allowing a range of angular adjustment about these axes when gluing to these surfaces. Examples of this type are found in U.S. Pat. Nos. 5,046,949 and 5,221,203. A drawback to this approach is that the articulators are typically more complex in design and are larger in size and material requirements, as they have to provide structure both above and below the models which makes this type more expensive to produce than the previous examples which can be affixed to the posterior surfaces of the models. A primary shortcoming found in all of these and all prior art one-use articulators observed and researched is the inability to properly allow for lateral and protrusive translatory motions between the articulated models.
An early dental related patent, U.S. Pat. No. 1743, dated Aug. 28, 1840, describes a dental articulator that has provision for xe2x80x9caction similar to that of the living subjectxe2x80x9d which is accomplished by using a sliding point of axis in the articulating joints to allow for these xe2x80x9clivexe2x80x9d translatory motions. Since then, many types and forms of dental articulators have been patented and manufactured ranging from extremely complex and expensive devices, to the more recent trend of using disposable or dispensable one-use articulators. U.S. Pat. No. 3,727,311 describes a very simple design connecting the models with a single resilient rod. This resilience allows translational motions, but this design lacks true hinging action. The previously mentioned U.S. Pat. No. 5,046,949 has a conventional hinge, but has no inherent.provision for allowing translatory motions.
An articulator in wide use today is disclosed in U.S. Pat. No. 4,449,930, which is a continuation-in-part to the previously mentioned 4,382,787, and U.S. Pat. No. 4,548,581 which discloses the same articulator. The articulators disclosed in the ""930 and ""581 patents attempt to allow functional translatory motions by having the technician flex bracket members connecting the models to the hinge. However, this flexing requires considerable force which inhibits the feel of the natural motion paths. Also, the forces of this flexing exacerbate the aforementioned weakness of the adaptive ball and socket pivot mechanism. Because this one adaptive element allows motions on any axis before immobilization and has to withstand the flexing forces of both hinge arms after immobilization, the adhesive required to immobilize these motions is very critical, since it must lock all of the axial forces and also fix the socket half of the pivot mechanism to the model. This requires that the adhesive used in the joints be of high quality and that its application be technique sensitive. If misapplied or if the glue is old or too high in viscosity, then failure of the adhesive within the ball and socket joint or between the model and socket becomes likely.
In U.S. Pat. No. 4,449,930 the socket half of the adaptive joint is incorporated into the model base which simplifies the design. However, molding the socket into the base is not practical since it would eliminate the ability to laterally align the sockets to set the hinge axis sagittally perpendicular. To make this design approach practical, the socket needs to be a separate piece to allow it a range of lateral placement on the model which requires another glue joint to fix the socket to the model base. There is described in a related patent U.S. Pat. No. 4,481,162 a mold which forms a slot in the rear of the dental model for receiving a corresponding key on the socket half of the joint.
A further improvement on this same design by the same inventor is disclosed in U.S. Pat. No. 4,734,033. This improvement specifically addresses translatory motion by making the hinge brackets more flexible but even with this enhancement the articulator fails to allow true sliding motions between the models, since there is still strictly a single axis rotational motion allowed by the hinge joints.
Translational motions are an extremely important function to be provided by an articulator in the task of fabricating dental prosthetics. The technician must be able to freely check all of the possible lateral and protrusive motions that the patient uses in mastication. If the technician is impeded in doing this, then invariably the prosthesis will need adjustment by the dentist during placement in the mouth (or perhaps even remanufacture) which results in considerable aggravation for the patient and dentist. None of the prior art one-use articulators have been found to be both simple of design (to allow inexpensive manufacture and thus dispensability) and permissive of true translatory motions.
This invention relates to dental model articulators as used in the fabrication of dental prosthetics to provide and allow respective movements between an upper and lower set of dental models representing the natural dentition of the patient. More particularly, this invention relates to one-use articulators and to a flexible mold for forming the base of a dental model to have a connection element of a pivot mechanism for mating with such articulators.
An object of the present invention is to provide an articulator that does not inhibit the replication of true masticatory motions between articulated dental models.
Another object of the present invention is to provide an articulator that is very simple and hence inexpensive to produce.
Yet another object of the present invention is to provide an articulator that is not technique sensitive in its implementation.
Yet still another object of the present invention is to provide an articulator that requires a minimal amount of material to produce but still achieves a strong broad connection to the models.
Yet a further object of the present invention is to provide an articulator that does not require locking more than one axis of an adaptive pivot mechanism.
A still further object of the present invention is to provide a design that provides fewer and stronger adhesive connections to the models.
Another object of the present invention is to allow articulation of models with a large variation of dimensional differences.
Another object of the invention is to provide a mold to facilitate the forming of a dental model base to include a connection element of a pivot mechanism for mating with an articulator.
The present invention is directed to a dispensable articulator for the production of dental prosthetics that provides an accurate relative positioning of a corresponding pair of dental model casts. In the discussion of prior art one-use articulators it was pointed out that multiaxial adaptation is a key feature in the design of this type of articulator. The essence of the present invention is to combine this multiaxial motion into hinge joints and to provide pivot mechanisms connecting the articulator to the models that require only one axis of adjustment and subsequent fixation. Eliminating the need to lock or fuse multiaxial motions in adaptive pivot mechanisms is a primary advantage of the present invention.
Aside from the obvious and inherent strength of these adaptive joints needing only a single axis of adjustment, their lineal nature also allows the adjacent halves of these mechanisms for each model to be laterally combined, incorporated into and made to span the width of the model thus allowing a wide range of lateral positional placement for the mating elements without requiring the additional glue interfaces that would be manifest if these were separate components.
Accordingly, a preferred embodiment of a dental model articulator for connecting upper and lower dental models includes an arm having first and second arm segments and an intermediate hinge joint for joining the first and second arm segments to provide hinging motion about a hinge axis. The first and second segments each terminates at a distal end in an arm connection element that is pivotally engageable with a model connector of one of the upper and lower dental models. Each arm connection element is pivotable about a single pivot axis. The hinge joint comprises a node and a pair of cymbals having opposing undersurfaces which include detents for receiving the node therebetween. The node is attached to one of the first and second arm segments at a proximal end of the respective arm segment. The pair of cymbals is attached to the other of the first and second arm segments at a proximal end.
According to another aspect of the invention, a flexible mold forms a dental model base that includes cylindrical connection elements of a pivot mechanism for mating with corresponding connection elements of an articulator. A portion of the pivot mechanism is integrated into the dental model to simplify the design of the articulator. The pivot mechanism is lineal in nature thereby allowing adjacent halves of the articulator to be laterally combined and made to span the width of the model. This combination provides for a wide range of lateral positional placement for the mating connection elements of the articulator without requiring additional glue surfaces that could be needed for separate components.
Accordingly, a mold for forming a dental model base includes a bottom portion having a rear wall and a side wall at a periphery thereof which extends upwards to define a cavity. The walls have upper edges which define an opening to the cavity. The mold further includes a shaping element for forming a connection element of a pivot mechanism at the dental model base which rotationally mates with a corresponding connection element of the articulator.